Non-linear pharmacokinetics of ofloxacin after a single intravenous bolus dose in pigs

The pharmacokinetics of ofloxacin (OFLX) was investigated after intravenous administration of 3, 10 and 30 mg/kg of body weight in pigs. Plasma OFLX concentration-time course collected from the highest dosage showed a convex decline, indicating a capacity-limited process in drug elimination (Michaelis-Menten elimination). Dose-normalized area under curve (AUC/Dose) and mean resident time (MRT) were dose-dependent, indicating a classical pattern of non-linear elimination pharmacokinetics. Based on simultaneous curve fitting from three doses, non-linear pharmacokinetic parameters were as follows: 0.87 mg/h/kg for maximum velocity, 2.20 microg/mL in Michaelis-Menten constant and 2.06 L/kg for apparent volume of distribution. Based on a model-independent analysis, the apparent volume of distribution at steady-state (Vdss) was dose-independent whereas total body clearance (CLtot) was dose-dependent, mainly contributed by renal clearance (CLr) with the regression line of CLtot=1.14xCLr+0.09 (r=0.92). The intercept of the regression line indicates non-renal clearance (CLnr), corresponding to the value of observed CLnr without dose-dependency. Because of a higher CLr compared with glomerular filtration rate (GFR) in spite of drug reabsorption, the CLr must contain the renal active tubular secretion. With increasing dosage, the level of saturation of tubular secretion of OFLX decreased the CLr, resulting in the decrease in CLtot. The plasma protein binding to OFLX was dose-independent: mean free fraction (fp)=0.73, with probably no influential effect on OFLX disposition. In conclusion, the degree of saturation in the renal active tubular secretion of OFLX could be a major causal factor in the alteration of CLr in an increasing dosage of OFLX. Accordingly, the alteration of CLr could directly induce the non-linear pharmacokinetics of OFLX in pigs, an important consideration in clinical therapeutics.     

Differentiation between bovine and ovine strains of Histophilus somni based on the sequences of 16S rDNA and rpoB gene

Nucleotide sequences of 16S rDNA and rpoB gene of 25 bovine and 6 ovine Histophilus somni strains were determined to detect subtle differences between the host animal species. The 1465 nucleotide residues of the 16S rDNA exhibited levels of sequence similarities of 99.4% or more. The high sequence similarity of the 16S rDNA of recently described species H. somni was confirmed in the 31 strains from cattle and sheep. These results suggested that the intra-specific diversity of 16S rDNA was limited in bovine and ovine strains of H. somni. The specific association of strains was also observed in the 311 bp region of rpoB gene which sequence similarities were 98.6% or more. However, the phylogenetic tree analysis of the rpoB gene showed that the ovine strains appeared to form a subgroup recovered in 70% of the bootstrap trees. In the 311 bp region of the ovine strains, a HincII restriction endonuclease site was detected. The PCR-amplified rpoB DNA of 46 bovine and 20 ovine H. somni strains were examined for the digestion with HincII. As the results, 17 strains of ovine strains were cleaved by the enzyme but none of the bovine strains appeared to possess the restriction site. The restriction enzyme analysis of rpoB gene may be useful to differentiate ovine strains from bovine strains of H. somni.     

Clinical features and rapid plasma reagin antibody titers in spontaneous and experimental rabbit syphilis

Rapid plasma reagin (RPR) titers were periodically examined during and after treatment in three rabbits clinically diagnosed with rabbit syphilis. RPR titers remained positive after clinical recovery and then gradually declined. Of the two rabbits inoculated experimentally, one showed clinical signs of the disease, while the other did not. RPR titers were also periodically evaluated before and after inoculation in these two rabbits. The trends in RPR titers reflected the course of infection, both in the spontaneous and in the experimental cases. An inapparent case and cases without clinical signs after clinical recovery showed low titers for long period of time. Useful information for interpretation of RPR titers measured clinically was obtained by this survey.     

Evaluation of hepatosplanchnic circulation and intestinal oxygenation in dogs with a condition that mimicked septic shock induced by continuous infusion of a low dose of lipopolysaccharide

OBJECTIVE: To determine whether continuous infusion of a low dose of lipopolysaccharide (LPS) to induce a condition mimicking septic shock in dogs would affect systemic and hepatosplanchnic circulation and oxygenation. ANIMALS: 12 healthy adult Beagles. PROCEDURE: Dogs received a low dose of LPS (Escherichia coli O55:B5) by continuous IV infusion at a rate of 1 microg/kg/h for 8 hours. Systemic hemodynamics; systemic oxygenation; blood flow in the cranial mesenteric artery, common hepatic artery, and portal vein; intestinal and hepatic tissue blood flow; mesenteric oxygenation; and intramucosal Pco2 were examined before and at selected time points after onset of the LPS infusion. RESULTS: After onset of the LPS infusion, cardiac index increased and mean arterial pressure (MAP) and systemic vascular resistance decreased, which is characteristic of the hyperdynamic state in septic patients. Hepatosplanchnic blood flow increased during the hyperdynamic state. Intestinal Pco2 was increased even when blood flows increased. During the latter half of the experimental period, MAP was maintained but hepatosplanchnic blood flows decreased and intestinal Pco2 increased further. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of the results suggested that hepatosplanchnic blood flow enters the hyperdynamic state during the early stages of sepsis and that intestinal tissue oxygenation is threatened even when hepatosplanchnic blood flow is increased or maintained. Hence, improvement of hepatosplanchnic circulation and intestinal tissue oxygenation is important in dogs with clinical evidence of a septic condition.     

Relationship between arginine vasopressin and high signal intensity in the pituitary posterior lobe on T1-weighted MR images in dogs

The posterior lobe of the pituitary gland (PL) normally shows characteristic high signal intensity (SI) on T1-weighted MR images (T1WI) in humans. The high SI is thought to represent storage of arginine vasopressin (AVP) in the PL. Normal dogs also show a high SI on T1WIs, but the origin is unclear. In the present study, we investigated whether the high SI in the PL on T1WIs in normal dogs is caused by AVP. We examined the SI in the PL on T1WIs, plasma AVP concentrations and plasma osmolality in normal dogs after excessive AVP secretion was induced by hypertonic saline overload. In addition, functional changes in the supraoptic nucleus and paraventricular nucleus of the hypothalamus under AVP secretion-stimulated conditions were examined immunohistologically. Under hypertonic saline overload, plasma osmolality and plasma AVP concentrations gradually increased, while the SI of the PL gradually decreased. This suggests that AVP secretion was stimulated by elevated osmolality. Moreover, there was a significant negative correlation between plasma AVP concentrations and the SI ratio of the PL. An immunohistochemical study of the hypothalamus nucleus revealed that AVP-immunopositive cells significantly increased in the hypertonic saline loaded dogs. We concluded that the high SI in the PL in T1WIs in normal dogs was caused by AVP stored at the site, and examination of the SI in the PL using MRI is useful for diagnosis of abnormal pituitary glands.     

Magnetic resonance imaging assessment of pituitary posterior lobe displacement in dogs with pituitary-dependent hyperadrenocorticism

The displacement and signal intensity (SI) of the pituitary posterior lobe were evaluated on T1 weighted magnetic resonance (MR) images in 28 dogs with pituitary dependent hyperadrenocorticism (PDH). Compared with normal dogs, the posterior lobe was displaced dorsally in the pituitary of the PDH dogs. Correlation between the pituitary height/brain area (P/B) ratio and the displacement of the posterior lobe in the PDH dogs suggests that dorsal displacement of the posterior lobe increases in accordance with enlargement of the pituitary. As to the SI of the posterior lobe, the PDH dogs showed significantly lower SI in comparison to the normal dogs. Taken together, these results suggest that assessment of the displacement and SI of the posterior lobe of the pituitary on T1-weighted MR images is useful for the diagnosis of pituitary adenoma. In pituitary microadenoma that presents no apparent tumorigenesis on MRI, evaluation of these values may be useful for diagnosis and selection of an appropriate therapy.     

Accumulation of phosphorylated repressor for gibberellin signaling in an F-box mutant

Gibberellin (GA) regulates growth and development in plants. We isolated and characterized a rice GA-insensitive dwarf mutant, gid2. The GID2 gene encodes a putative F-box protein, which interacted with the rice Skp1 homolog in a yeast two-hybrid assay. In gid2, a repressor for GA signaling, SLR1, was highly accumulated in a phosphorylated form and GA increased its concentration, whereas SLR1 was rapidly degraded by GA through ubiquitination in the wild type. We conclude that GID2 is a positive regulator of GA signaling and that regulated degradation of SLR1 is initiated through GA-dependent phosphorylation and finalized by an SCF(GID2)-proteasome pathway.     

Trilostane-induced inhibition of cortisol secretion results in reduced negative feedback at the hypothalamic–pituitary axis

Cushing's disease caused by pituitary corticotroph adenoma in dogs is usually treated by medical treatment, and the efficacy of this treatment has been reported. However, controversy remains as to whether reduced negative feedback through the inhibition of cortisol secretion, similar to Nelson's syndrome, may appear as an adverse effect. The purpose of this study was to investigate the effect of reduced negative feedback through the inhibition of cortisol secretion by daily trilostane administration on the pituitary–adrenal axis in clinically normal dogs. Dogs were administered 5 mg/kg trilostane twice a day every day for 8 weeks (n = 8) or 16 weeks (n = 3). After the initiation of trilostane administration, plasma adrenocorticotropic hormone (ACTH) concentrations were increased remarkably. As assessed by magnetic resonance imaging (MRI) during administration, the pituitary became enlarged. After trilostane administration, the cytoplasmic areas of the pituitary corticotrophs were increased and the ratio of pituitary corticotrophs to all cells in the anterior lobe was greater in the trilostane-treated dogs than that in untreated animals. In addition, histological examinations revealed bilateral adrenal cortical hyperplasia. Using real-time PCR quantification, the expression of proopiomelanocortin (POMC) mRNA in the pituitary and ACTH receptor (ACTH-R) mRNA in the adrenal gland was greater in the dogs treated with trilostane than in untreated dogs. These results indicate that reduced negative feedback induced hyperfunction of the pituitary corticotrophs and pituitary enlargement in healthy dogs. These changes suggest that the inhibition of cortisol secretion by trilostane may increase the risk for accelerating the growth of corticotroph adenomas in dogs with Cushing's disease.